The present invention relates to grinding mills, and particularly to bowl-type grinding mills incorporating in a mill cylinder a decelerating means, a grinding roller means, a classifying means, and a finished product conveying means. A motor drives the said means by a single shaft. This mill is suitable for efficiently grinding materials such as soft or hard ores (e.g. coal for power plant, or ore for making cement), viscous material, or fibrous material, to a desired fineness.
Typical of known roller mills is the Raymond ring-roller mill, which is vertically mounted and contains therein a centrifugal grinding roller device and a fixed separator. The grinding roller device is operated by a drive means mounted outside the mill through a speed reducing means, drive means, and a horizontal drive shaft. A blower, also mounted outside the mill, is used for creating an upward air stream in the mill to sweep finely ground material or particles through the fixed separate vanes of the separator into a discharge pipe. Such a mill is rather complicated in construction and difficult to maintain and repair. It also occupies a large space, and requires high power. In operation the mill presents further problems such as vibration, noise, and dust clouds. Moreover, as far as grinding efficiency is concerned, particles finer than 300 U.S. standard mesh can hardly be produced, and grinding fibrous and viscous raw materials can be difficult.
In order to overcome the above disadvantages, the inventor provides the kinds of improved roller mills that were described in U.S. Pat. Nos. 3,955,766; 2,112,359; 2,431,746; 4,483,487; 2,909,330; and 4,682,738.
In U.S. Pat. No. 3,955,766, mounted in ascending order in this roller mill are a speed reducer device, a centrifugal grinding roller device, a classifier device and dust collector device. All the devices are driven by a single vertical shaft that is driven by an electric motor mounted on top of the mill so as to obviate the need for a drive means, driven means and blower located outside the mill. This not only renders the mill simple in construction and compact in size, but can also increase grinding efficiency. Furthermore, the roller mill is suitable for grinding various raw materials including solid, fibrous, and viscous materials, with the finished particles being finer than 1,000 mesh.
While that roller mill enjoys several advantages over the previously described ring-roller mill, the inventor has performed subsequent experiments and has found that although there is no denying the fact that using centrifugal force resulting from rotating rollers as the grinding force yields positive grinding effects, the centrifugal force varies in accordance with the rotational speed and weight of the rollers and thus may result in different grinding forces. Under normal low-speed operating conditions, the rollers will not cause any problem. However, if the rotational speed of the rollers is increased in order to facilitate grinding of the raw materials or to obtain greater capacity or output, an excessively high grinding pressure results from the increased centrifugal force due to the increase in rotational speed of the rollers. The excessively high grinding pressure tends to compress part of the ground fine particles into flakes which may adhere to the grinding ring and the peripheral wall of the rollers or drop down on the bottom of the mill instead of being carried in an air stream to the classifier. Also, the excessively high grinding pressure often gives rise to great vibration, noise, and wear of the rollers and the grinding ring by subjecting both to crushing and friction. In addition, since there is no clearance between the centrifugal rollers and the grinding ring and relatively high power is required to start operation due to the great friction and vibration at the time of actuation. Especially, in case of an unexpected loss of power during operation, it will be extremely difficult to re-start the rollers after the power supply resumes unless the raw material already fed into the mill has been cleared away, since the internal working parts of the mill are fully loaded. In addition, since the aforesaid rollers are each held in suspension by a support arm, when the rollers need repairing or replacing due to wear, the support arm and the shaft of the associated roller must be disassembled as a whole so that roller can be removed, thus inconveniencing maintenance and repair work. Further, the support arm occupies so large a space that not only is the effective working space in the separation chamber diminished, but the support arm, when rotating, also hinders the formation of an upwardly spiralling flow of ground particles and air below it to such an extent that the particles come together and cause the grinder to become plugged.
U.S. Pat. No. 4,682,738 disclosed a vertical centrifugal ring-roller mill comprising among others, a grinding roller means having many elements which are rotated as a unit. The pressure of grinding is determined by the speed of the rotation of the roller means and the weight thereof. When maintenance is to be done, the whole grinding mill must be stopped in order to inspect the amount of oil and degree of wearing in the grinding rollers. This is time consuming and inconvenient. The amount of oil and degree of wearing cannot be monitored externally.
Therefore, the main object of the present invention is to eliminate the above mentioned disadvantages by providing a kind of bowl-type grinding mill comprising mainly a decelerating means, a grinding roller means, means for adjusting the clearance between grinding ring and rollers, a classifying means, a finished product conveying means, a motor, and a transmission means, wherein the grinding rollers and the grinding ring can be of different degrees with respect to a center axis of the grinding mill to 90.degree. or other appropriate degrees according to the rotating speed and the horsepower of the grinding mill, and moreover, the assembly, maintenance, adjustment, or the replacement and adding of the oil is all made easy.
Another object of the present invention is to provide a bowl-type grinding mill, wherein the classifying means comprises a plurality of separate blades which are disposed obliquely and radially and positioned easily so that ground particles and air can pass through the separate blades perpendicularly and the separation thereof is made easy.
A further object of the present invention is to provide a grinding mill, wherein a spring or hydraulic device for pressurizing a pressure plate is provided outside of a grinding mill cylinder so that the pressure of the grinding rollers (i.e., the clearance between grinding ring and rollers) can be adjusted externally during operation and such that the efficiency of grinding can be raised and the wear of the parts can be reduced.
Still another object of the present invention is to provide a grinding mill, wherein a grinding roller support plate is provided in the grinding mechanism, the support plate can also serve as an oil reservoir, an oil inspection stick is provided on the upper part of the support plate, a transparent glass is provided on the lower part of the support plate so as to monitor the amount of oil in the grinding mechanism.
Another object of the present invention is to provide a grinding mill, wherein the grinding ring comprises several grinding ring pieces, said pieces are positioned in an annular grinding ring seat with wedge-shaped fixing blocks which are secured to the seat with several nuts, with the leading end of the nuts approximately facing radially outwardly and thus the nuts will not be loosened during operation, and on the contrary, will be fastened more tightly because of the pressurizing force imparted thereupon by the grinding rollers and the eccentric force imposed thereupon during operation.
Another object of the present invention is to provide a grinding mill, wherein the motor is horizontally fastened to one lower side of the mill and exerts a force to the mill through a vertical main shaft which extends along the axis of a grinding mill cylinder.
Another object of the present invention is to provide a grinding mill which is simple in construction, compact in size, occupies a small mounting area, requires low power, starts easily, and creates a minimum of noise and vibration.
A further object of the present invention is to provide a grinding mill in which the main transmission mechanism and grinding roller means are placed outside of the mill cylinder and a classifying chamber is formed in the upper portion of the mill cylinder and a classifying chamber is formed in the upper portion of the mill cylinder so that the mill has a low center of gravity and smooth, uninterrupted flow of ground particles and air is ensured.
Another object of the present invention is to provide a grinding mill, wherein there is no mechanism above the rollers which may hinder the assembly and disassembly of the rollers or the separation of ground particles and air.
Another object of the present invention is to provide a grinding mill suitable for grinding solid (ores), fibrous and viscous raw materials.
Another object of the present invention is to provide a grinding mill which enables the user to grind the raw material to the desired fineness by adjusting externally the clearance between grinding ring and rollers while minimizing noise and vibration.